1. Field of the Invention
The present invention relates to a device for driving various accessories such as an alternator, a cooling water pump or the like, utilizing power of an engine of an automobile or the like.
2. Description of the Prior Art
In an engine of an automobile or the like, accessories such as an alternator, a cooling water pump, an air-conditioning compressor, an oil pump for hydraulic servo steering or the like are belt-driven by a crank pulley installed at an end of a crank shaft. Since the accessory drive is accompanied with large power loss during the high speed running of the engine, in order to avoid it, various methods have been proposed that gear shifting of a crank pulley is performed with respect to the engine rotational speed and the running speed of the accessory is limited.
In FIG. 3 illustrating an accessory drive device having such speed limiting function in the prior art, numeral 1 designates an input shaft directly coupled to a crank shaft of an engine (not shown), numeral 2 an input transmission member on the input shaft, and numeral 3 a cam device for generating pressure interposed between the input shaft 1 and the input transmission member 2. Numeral 4 designates a plurality of planetary cones, each composed of a frictional transmission surface 4a on a conical surface, a frictional transmission surface 4b on a bottom surface of the cone, and a frictional transmission surface 4c on a circumferential surface of the cone axial line. Numeral 5 designates a shifting ring which is engaged in frictional engagement with the frictional transmission surface 4a of the planetary cone 4 and moved in the axial direction so as to vary the frictional transmission radius of the planetary cone 4, and numeral 6 an orbit ring which is engaged in frictional engagement with the frictional transmission surface 4c of the planetary cone 4 and, in its non-rotation state, guides the revolution of the planetary cone 4 around the axis of the input shaft 1. Numeral 7 designates an accessory drive pulley, numeral 7a a plurality of key grooves on the inner circumferential surface of the pulley 7 in the axial direction, and numeral 8 a roller key which transmits the rotational force of the shifting ring 5 to the pulley 7 and suppresses the movement in the axial direction and is engaged with the groove 7a. Numerals 9, 10 designate side plates to support the pulley 7 at both ends. Numeral 11 designates a stationary plate which fixedly supports the orbit ring 6 and is fixed at a mounting part 11a to the stationary member of the engine (not shown). Numeral 12 designates a frictional transmission oil which acts as a medium for the frictional transmission and is filled in the space enclosed by the pulley 7, the side plates 9, 10 and the input shaft 1 and sealed by oil seals 13, 14, 15. Numeral 16 designates a centrifugal governor comprising a centrifugal weight 16a and a spring plate 16b which supports the centrifugal weight and connects it to the shifting ring 5, and numeral 17 a return spring.
Operation of the accessory drive device will be described. The rotational force of the crank shaft of the engine is transmitted to the input shaft 1, and then to the input transmission member 2 through the cam device 3. The planetary cone 4 performs the self-rotation on its own axis, and at the same time performs the revolution around the axis of the input shaft 1 along the frictional transmission surface of the orbit ring 6 which is stationary. The shifting ring 5 engaged in frictional engagement with the frictional transmission surface 4a of the planetary cone 4 is rotated around the axis of the input shaft 1 on the basis of the differential action between the self-rotation and the revolution of the planetary cone 4 and the transmission radius ratio, and drives the pulley 7 through the roller key 8. The rotational speed ratio between the input shaft 1 and the gear shifting ring 5 can be arbitrarily set by moving the shifting ring 5 in the axial direction so that the effective radius ratio of the frictional transmission between the input shaft 1 and the shifting ring 5 is varied. For example, if the shifting ring 5 is engaged in frictional engagement at the large diameter side of the planetary cam 4, the rotational speed ratio becomes 1:1, and at the small diameter side, i.e., near vertex of the cone, the rotational speed ratio becomes 1:0.4; thus reduction at the shifting ring 5 can be selected in nonstage state. The centrifugal governor 16 controls the axial position of the shifting ring 5, and automatically controls the rotational speed of the pulley 7 to the speed ratio 1:1 at the low speed state of the engine and to the nearly constant rotational speed when the engine is at an intermediate or high speed state. The frictional transmission oil 12 is interposed on the frictional transmission surface and acts as medium for the frictional transmission force and performs lubrication and cooling of the contacting surface and the bearing.
In the accessory drive device utilizing the continuously variable transmission with the planetary mechanism of frictional transmission type as above described, the frictional transmission oil is infused in the device and a small number of air bubbles may be expanded by heating during the running and generate a high pressure within the enclosed space. In this case, since any of the oil seals 13, 14, 15 cannot endure the high pressure and oil leakage may occur, a special seal high withstanding pressure must be used. As a result, the device becomes of large size and high cost, and the seal of high withstanding pressure usually produces large sliding loss and may deteriorate the transmission efficiency of the device.
An object of the invention is to provide an accessory drive device wherein a even if the frictional transmission oil and bubbles are expanded by heating during running, pressure within the device can be automatically adjusted so that it does not rise.